The Community Impact of Post-Earthquake Safety Decisions Based on Damage to Tall Buildings and Elevated Hazard Due to Aftershocks

A key component of community resilience is the ability to recover community functions after an earthquake. Resilience planning focuses on identifying critical functions, setting recovery time targets for various hazard levels, and assessing the gap between the desired and the anticipated performance. These performance assessments should consider all potential disruptions to community functions, such as damage that makes buildings unsafe, damage to equipment and architectural finishes that makes buildings non-functional, and loss of utility services or transportation access. A recovery-based assessment includes both the initial loss of functionality and the process for restoring it, including stabilizing unsafe buildings and securing the necessary resources to initiate building repairs. A heavily damaged building has an elevated risk of collapse during an aftershock, endangering the occupants in nearby buildings. Post-earthquake safety inspectors evaluate which damaged buildings to red tag and where to set up safety cordons, restricting access to potential fall zones. This dissertation focuses on these access restrictions associated with unsafe buildings.
Post-earthquake decisions regarding which buildings are safe to re-enter are an important part of a community’s recovery process. Unsafe buildings and neighborhoods should be marked as such, alleviating the public’s uncertainty as they take stock of their surroundings. However, these decisions should be made carefully, recognizing their impact on the community. Displacing too many residents through overly conservative red tagging would increase the potential for permanent outmitgration. Businesses in an inaccessible downtown may fail or need to relocate–to the outlying areas or to another city. Therefore, while safety cordons are imperative, their presence should be minimized where feasible, either by building retrofits to proactively reduce the likelihood of earthquake damage or by facilitating building inspection and stabilization efforts to remove the cordons as soon as possible. This dissertation proposes tools for quantifying three aspects of access restrictions: the additional community downtime due to safety cordons, the reduced safety of a damaged building, and the elevated risk of building collapse in the presence of aftershocks.